For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

How old is the Master Cylinder in your car? I have a car that I finished a few days ago and the clutch working only when it wants to, We are changing the master cylinder today and that should fix the problem. You have to remember, the factory MC is on the very end of the scale of fluid movement for this slave cylinder.

My clutch MC is a new stock unit. Since my car was sitting for 10 years prior to the start of the swap I ordered a new one.

Re. a shim - my pressure plate is from ACT, I called them last week and they said my pressure plate does not require a shim, it's a direct replacement for stock components. The slave is sitting against the pressure plate fingers when the clutch peddle is released, so there is no wasted slave travel.

I have not checked to see if the firewall flexes any but I did look closely at the firewall when I swapped the MC and did not see any cracking. I can check with a helper tonight.

So I can try another stock MC (I have another one sitting in my garage) or try a Wilwood 13/16 unit, or????

My firewall looks great, but flexes. Another symptom of the flexy firewall is a heavy clutch pedal. I put in a brace I made out of angle iron and it fixed it 95%. The pedal is now easy and there is minimal movement from the clutch MC. If yours is flexing that may account for the issue.

I thought I'd post my final solution for others who might be in the midst of a swap. Instead of trying another stock clutch MC, I ordered and installed the Wilwood 13/16 unit and I'm happy to report it gave me enough slave movement to release the clutch correctly. I plan to paly a bit more with the input rod to see if I can get it to engage a bit higher in the pedal travel, but it works and I can drive the car. One other change I made was switching to Red Line MT90 like someone else had suggested. It does seem to help the syncros and speed up the shifter movement from gate to gate. I guess Mobile 1 synthetic gear lube was not the best for this transaxle.